Light emitting diode, namely, LED technology has been receiving huge attention as eco-friendly technology. White LED technology has been growing annually approximately by 50% over the world. With the development of LED technology, the prospects of LEDs taking the place of fluorescent lights and other lighting apparatuses are getting real.
Recently, an LED lighting apparatus shows a tendency of using 1 W or more output LED package, which is higher-output than a plurality of low-output LEDs, to reduce the number of LED mounted therein.
In a bulb type lighting apparatus may be mounted approximately 70 or more light emitting diodes with 0.5 W output. In a straight type lighting apparatus may be mounted approximately 400 or more light emitting diodes with the 0.5 W output as an example of a lighting apparatus using the low-output LED. If the lighting apparatus is fabricated with low-output LEDs mounted therein, there are several advantages in lighting efficiency or functional improvement.
However, to mount a number of low-output light emitting diodes in a lighting apparatus at low cost, manufacturers has to use the LED package manufactured with their own technology and the mounting process has to be performed in existing equipment possessed by the manufacturers. Because of that, most manufacturers incapable of manufacturing the LED packages tend to use high-output LEDs for manufacturing lighting apparatuses to prepare LED packages and to reduce the mounting cost of the LED packages.
When the high-output LED is used for a lighting apparatus, heat emission will be a problem. If the high-output LED is used for a lighting apparatus, a light emitting part is concentrated on and the temperature happens to increase accordingly. In addition, brighter and brighter lighting has bee preferred and the absolute quantity of heat has been increasing.
Especially, outdoor lighting is showing such a trend such as a streetlight and a fishing lamp. If the temperature of the LED increases, a forward voltage of the LED decreases and luminescence efficiency deteriorates with a shortened life span of usage. In case of using a high-output LED that reaches a high temperature status easily, an expensive material having a heat-resisting property has to be used in the LED package and this leads to another cost increasing factor.
To solve the heat emission problem, LED lighting apparatuses that use a metal base substrate have been proposed. However, it cannot be said that even the metal base substrate has a sufficient heat emission property. A ceramic substrate formed by printing silver-paste in an aluminum nitride (AlN) plate with high heat conductivity has bee known as substrate for the high-output LED. However, AlN has a disadvantage of high production cost.
There has been an attempt to enhance heat emission by improving a substrate structure of an LED package. As another attempt, a mechanical structure of an LED chip is improved to enhance the heat emission. However, such methods cost much disadvantageously.